No abstract

In this study, we demonstrated a straightforward method for the easy access of chromeno[4,3-b]quinolin-6-ones via a onepot three-component reaction of 4-hydroxycoumarin, aldehydes and aryl amines in the presence of halloysite nanoclay as an eco-friendly, inexpensive and green heterogeneous catalyst under solvent-free conditions. Moreover, symmetric and unsymmetric bis-chromeno [4,3-b]quinolin-6-ones were obtained from dialdehyde or diamines in good yields by this method. To date, this is the first report on the synthesis of symmetric and unsymmetric bis-chromeno [4,3-b]quinolin-6-ones via such a one-pot, multicomponent reaction. Some prepared chromeno [4,3-b]quinolin-6-ones displayed as interesting fluorophore compounds, hereupon their fluorescence properties were considered. Good to excellent yields, short reaction times and avoidance of toxic solvents are the significant features of this green procedure.

In this study, a new and stable Ce(IV) immobilized on halloysite nanotubefunctionalized dendrimer was designed, synthesized, and characterized using Fourier-transform infrared, elemental analysis, thermogravimetric analysis, field emission scanning electron microscopy, scanning electron microscopyenergy dispersive X-ray spectroscopy, transmission electron microscopy, dynamic light scattering, Brunauer-Emmett-Teller, and inductively coupled plasma optical emission spectroscopy techniques. This catalyst was efficiently used for the one-pot, single-step multicomponent synthesis of pyrido[3,2-c] coumarins from 4-aminocoumarin, aldehydes, and aryl ketones. The efficiency and selectivity of this catalytic system were also evaluated for the synthesis of pyrido[3,2-c]coumarins from terminal/internal alkynes instead of aryl ketones. In this respect, the regioselectivity of the products was successfully assigned by X-ray crystallographic analysis. All these reactions were best performed under solvent-free conditions in the presence of only 0.28 mol% of the catalyst, and such a one-pot multicomponent synthesis of pyrido[3,2-c]coumarins is reported for the first time. It is also worth noting that single-step and short reaction path for the synthesis of a variety of pyrido[3,2-c]coumarins along with excellent reusability of this dendritic catalyst makes this method economically and environmentally attractive.

Nano Ag/ZnO as a heterogeneous catalyst for the oxidation of benzylic C–H bonds in air was demonstrated.